A novel out-of-plane MEMS tunneling accelerometer with excellent low frequency resolution

After successful fabrication and characterization of the first ICP based tunneling accelerometer, we modified the fabrication process to eliminate the knife-blades on the beam, which is caused by the double mask ICP process. These changes have resulted in about 20% yields enhancement at the open-loop characterization phase. The new process also enhances the height of the proof mass without increasing the aspect ratio. During the characterization, output saturation is observed which is caused by the variation of the tunneling voltage with the tunneling current. It deteriorates the resolution of the accelerometer at the same time. A new feedback circuit is designed in which the tunneling voltage is kept constant. The accelerometer is tested in the low noise environment and the result shows excellent low frequency resolution, which is 15 mug/rtHz (from 1 Hz to 100 Hz). Different tip areas are fabricated in this experiments and the open loop characterization shows no obvious relation between the happening of the tunneling current, the barrier height and the tip area.